Catalytic Hydrogenation of N‐protected α‐Amino Acids Using Ruthenium Complexes with Monodentate Phosphine Ligands

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AbstractA ruthenium complex with a monodentate phosphine ligand was used to catalytically hydrogenate N‐protected α‐amino acids under essential retention of the configuration of their α‐chiral centers. Among the ligands tested for this hydrogenation, which proceeds at a relatively low temperature, tris(para‐fluorophenyl)phosphine exhibited the best performance. In comparison, electron‐rich monodentate, bidentate, and tridentate phosphines were far less effective. The precatalyst Ru(OAc)2[(p‐FC6H4)3P]2 was synthesized and isolated, and its structure was determined by a single‐crystal X‐ray diffraction analysis. N‐protected α‐amino acids with neutral alkyl side chains, including polar functional groups such as sulfides, indoles, ethers, phenols, pyrroles, and arenes, are compatible with the applied hydrogenation conditions, affording the corresponding optically active 2‐substituted‐2‐(1H‐pyrrol‐1‐yl)ethan‐1‐ol (2‐amino ethanol) derivatives in moderate to high yield.magnified image